The overall objectives of our research are to determine what role, if any, nitrite and nitroso compounds play in the etiology of human cancer. Toward this end, we have now developed a number of tools and experimental systems capable of measuring the flux of precursors and the quantity of endogenous synthesis of compounds related to nitroso carcinogens in man. In the coming year we will continue our studies on the endogenous synthesis of nitrate and its precursors using N15 as a biochemical tracer. Studies will also continue on the amount and types of N-nitrosoamino acids excreted by humans in urine and on the modulation of formation of nitroso compounds in the ferret and dog stomach. In addition to the excreted nitrosamines we will continue to measure the flux of methylamines and their endogenous synthesis from precursors such as choline. In the area of carcinogenic precursors the research will stress the chemistry of indoles as potential gastric mutagens and carcinogens. Attempts will also continue to identify factors in gastric juice which promote nitrosation and naturally occurring substances which inhibit nitrosation. We will continue to develop and refine the rat as a model for developing short-term tests for risk factors for gastric carcino-genesis. Studies will begin on the identification of mutagens from nitrosated black beans and from salted fish.